Concentric resonant line and circuit therefor



June 17, 1941. N. E. LINDENBLAD ,597

coucmmxc RESONANT LINE AND CIRCUIT THEREFOR Filed Aug. 25, 1938 s Sheets-Sheet 1 INVENTOR. N/LS E. L/NDENBLAD \BY I 5, 5W

- AT ORNEY.

' June 17, 1941. UNDENBLAD 2,245,597

CONCENTRIC RESONANT LINE AND CIRCUIT THEREFOR Filed Aug. 25, 1958 s Sheets-Sheet 2 0UTPUTI U MASTER Z 05c RESO/VAN T LINE R. E NEU TRAL/ZED PUSH-PULL AMPL.

FREQUENCY MODULA TOR RJ-Z AMPL.

OUTPUT RE AMPL. I

FREQUENCY MODUL A TOR REC7/F/ER\ uooum TOR CHOKE com I 'INVE'NTOR;

N/LS E. LINDENBLAD ATro NEY.

June 17, 1941.

N. E. LINDENBLAD. CONCENTRIC RESONANT LINE AND CIRCUIT THEREFOR Filed Aug. 25, 1933 3,Sheets-Sheet 3 RE AMPL lF/ER k/EAMPL IFIER D 7 R x 0 E m 0 m H II", A E w M a W W Patented June 17, 1941 I coNoENrnIc RESONANT m AND CIRCUIT 'rnannron Nils E. Lindenblad, Port Jefferson, N. Y., assignor to Radio Corporationot America, a corporation of Delaware Application A gust 25,1938, Serial N... 226,674

16 Claims. The present invention relates to improvements in tuned circuits, particularly concentric resonant lines, and to circuits therefor. k Tuned circuits in the form of concentric resonant lines are used particularly in connection with short and ultra short wave circuits. These lines are, because of their construction, nonradiating in character, and arecharacterized'by low loss. be used in any one or more of the following capacities: As the frequency determining element of an oscillator; as an output tank circuit; as a tuned interstage coupling circuit; and as a filter. For a complete description of concentric resonant lines, reference is made to United States Patent No. 2,120,518, granted June 14, 1938, to John F. Dreyer, .Jr.; United States Patents Nos. 2,108,895 and 2,077,800, granted February 22, 1938, and April 20, 1937, respectively, to Fred 'H. Kroger; and to the article by Clarence W. Hansen en- -titled Resonant lines for frequency control, published August, 1935, in Electrical Engineering," pages 852 to 856.

One of the objects of'the present invention is to enable a multiplicity of voltage connections to be made to a resonant line withoutdisturbing its balance or introducing multiple degrees of freedom. Y

Another object is to provide 'an improved concentric resonant line and vacuum tube circuit which has substantially one degree of freedom.

A further object is to provide an improved oscillation generator circuit having a concentric resonant line as a frequency controlling element therefor, wherein there is reduced the possible number of modes of oscillation (i. e., degrees of freedom).

Briefly stated, the improved concentric resonant line of my invention comprises an inner and an outer concentric conductor suitably coupled together to provide a tuned circuit in-generally known manner, with the addition of a pinrality of separated metallic condenser plates sandwiched between the inner conductor and the outer conductor to provide condenser-layers ,of 45 diiferent capacity. These condenser plates may have the form of discs located in the general line of extension of the inner conductor and whose planes are transverse of the longitudinal axis of the inner conductor, or they may be natal-- lel to the longitudinal axis of the inner conductor.

One advantage of the improved concentric resonant line of the present invention is that the line can be terminated with discor cylindrical Such tuned circuits, it is known, my

condensers, thus providing extremely short and low reactance connectionsto the vacuum tube elements associated with the line. One way of accomplishing this is to widen the discs'beyond 5 the normal width of the inner conductor and to attach the electrode terminals of the associated vacuum tubes directly to these discs. The principles underlying the present invention are explained in more detail in the followl0 ing description which is accompanied by draw- 15 tron discharge device circuits;

push-pull electron discharge device oscillator circuits; I

Figs. 7 and .8 respectively illustrate my im- 30 proved concentric line used as voltage step-down andstep-up interstage coupling elements; and

Fig. 9 is a perspective view of a physical embodiment of one of my improved concentric resonant lines and associated vacuum tube circuits.

Referring to Fig.1. there is shown a conconnected together at one of their adjacent ends by an end plate 3. Inner conductor 2 is capaci- 0 tively coupled at its other end to the outer conductor by virtue of a metallic plate 4 suitably spaced from end plate I. In the space between plates 4 and 5 there are interposed separate'd;

metallic discs or plates 6 and I, suitably mounted on insulating supports, not shown. It will thus be appreciated that the capacity between plates 4 and 5 is divided up into several series capacities by means of discs {and I sandwiched be.--

tween 4 and I.

The voltage distribution of; the resonant line Y will enable making connections thereto without introducing-multiple degrees of freedom, 1. e

itive and that the connection between them and the ,condenser plates can be. made extra short and therefore ,of negligible inductance. The thermionic'electron discharge devices, together with the sandwiched capacity plates, then form a system which is essentially capacitive. The

resonant line has thus only one degree of free modes of oscillation. The reason for this is thatthe vacuum tube elements themselves are capac- 2', 2' are metal discs 8, 9 and l0, suitab1y s'paced apart and 'insulatingly mounted in a manner not shown. The voltage distribution of the concen: 'tric line of Fig. 2 is indicated by the dotted line V, It should be noted that the central disc 9 is at a voltage node or zero gradient point while the discs and rods on opposite sides thereof have voltages of opposite, phase.

' Fig. 3 shows a concentric resonant line of the type shown in Fig. 1 connected to a vacuum tube oscillator II. The grid of the tube H is connected by way of example to plate 4; while the cathode of tube ll iscon'nected to plate 1. Output energy is obtained from plate I2. A positive polarizing potential for the anode of the oscillator II is derived fromsource +Ep, and suitable bias for the grid is obtained by virtue of the connection consisting of choke l3 and resistance i4 placed between grid and cathode. The cathode is connected to ground through a choke i5; and the anode connected to ground by low reactance connection between the same and the associated vacuumtube electrodes. The outer conductor 24 is enlarged at its center portion to accommodate the wide plates 28, 29 for completely shielding same. 1

The dotted line passing between the plates 28, 29 indicates a space 01' zero voltage relative to the metallic plates on both sides thereof. This dotted line is marked zero (0). Plates 21 and 29 are marked minus while plates 26 and 28 taneous relative polarities thereon at a given moment. During another portion of the cycle, the polarities on these plates will, of course, be reversed.

The circuit of Fig. 5 shows a master oscillator comprising a pair of vacuum tubes 30, 3| connected in push-pull relation to the tuned concentric line 24, 25, the latter of course controlling the frequency of operation of the oscillator tubes. The grids of tubes 30 and;3l are connected conductively to plates 28, and 29 to provide voltages of opposite instantaneous relative phase on the 1 two grids. Similarly,the anodes of the tubes 30 25- and3l are capacitively coupled to plates 21 and 26 by virtue of small plates 32 and 33 suitably spaced from 'plates 21]; and 26, respectively. These small plates 92 and 33, as well as condenser discs 29 and 28, are insulatingly mounted in the interior of the concentric line in suitable'manner, ,not shown. Connections 94 and 35 supply positive polarizing potentials to the anodes of the oscillator tubes from the positive terminal 'of, a source +Ep.

v The master oscillator is arranged to drive a neutralized push-pull radio frequency amplifier v comprising a pair of vacuum tubes 96, 31, whose means of the blocking and by-pass condenser l9.

The system of Fig. 3 can be likened to the well known Hartley circuit, wherein a-tuned circuit, in this case the concentric line, is connected between the grid and anode of awacuum tube whose. 4

cathode is connected to anintermediate point ori the inductance of the tuned circuit. The anode end of the tuned circuit is here grounded for radio frequency energy.

Fig. 4 shows how metallic cylinders. arranged in parallel can be employed instead of. discs to obtain my improved concentric resonant line.

- The resonant line consists of an outer conductor,

i and an inner conductor l1. One end of the inner conductor I1 is shown enlarged at "to \increase the capacity existing between the con-1 doctors of the line. A multiplicity of cylinders I9, 29 and 2| placed between the enlarged end 19' and the side walls of the outer conductor serve to subdivide the capacity therebetweerr lnto series condensers, in a manner similar to the ar-- rangements of Figs. ,1 and 2. A'pair of electron discharge device oscillators 22 and 23' are shown connected'inparallel relationto the concentric line, whereby said line functions to stabiiize or control the frequency of oscillations produced by both vacuum tubes. i I

C Fig. 5 shows how a-concentric line of the general type of Fig. 2 canbe used in connection with composed of an outer conductor 24 and an inner conductor'comprising a pair of separated coaxial rods 25, 25 capacitively coupled together at adjacent ends by mean s'of plates 26, 21. -Inter-' posed between plates 26 and Hare a pair ofseparated and relatively wide condenser discs or plates 29 and 29. Discs or plates28 and 29am wider than plates 26 and 21 to provide a short and anode and 'grid electrodes are capacitively interconnected in known bridge fashion for neutralization purposes. The grids of the amplifier tubes are capacitively connected to plates 29 and 29, by virtue of connections. and 39, in turn connected, respectively, to small capacityplates l9 and 4i. These last connections insure the application of opposite relative polarities at all times to the grids of the tubes 38,-.31. Suitable negative bias potentials, indicated, by I the minus sign, are applied to the grids of the amplifier tubes, whilea positive polarizing potential applied to-the midpoint of the output tuned'circuit." insures the application of a -a. push-pull circuit. The resonant line is here suitable voltage to the anodes-of the amplifier tubes. I A

Dueto-t he fact thatplates 28and 39 are wider than normal, the'oscillatorand amplifier tubes can be mounted on the enlarged central portion of the outer conductor, or if desired, directly on the plates 29; 29 tovinsure minimum lengths of leads between tubes and plates, and thus obtain short and low reactance connections. It is also possible-to directly attach the tube electrodes to the capacity plates.

Fig. 6 shows how my improved concentric line,

' of a type similar to that shown in Fig.5, can be incorporated. in .;a unit providing either amplitude or frequency modulated output. In this. figure a master oscillator comprising a pair of push-pulL vacuum tubes 43, 44 drives a radio frequency push-pull neutralized amplifier com- 'their prising apair or vacuum tubes l5, 46. Output energy from the amplifier is derived from tuned circuit 41. Formodulating the output there is ,provided a pair of modulating tubes 48, 49. By throwing the switch 50 to the left, the output energycan be amplitude, modulated, while 'i're- "are marked positive to indicate the instansaid plates being insulated froni'each other and quency modulation can be obtained by throwing this switch to the'right. When amplitude modulation is desired, only the oscillator and the radio frequency amplifier are energized. The

radio frequency amplifier is t en modulated. When frequency modulation is desired, the feed back or frequency modulator is also energized.

The modulator is then connected to modulate the feed-back of the frequency "modulator." The radio frequency amplifier is then not modulated but operates asa straight amplifier.

Fig. 7 indicates howthe improved concentric resonant line of the type generally shown in Fig. 2 canbe used as an interstage coupling element to step down the voltage between the output ofradio frequency amplifier stage 5 l and the input of radio frequency stage 52, each stage comprising a pair ofvpush-p'ull connected eleetron discharge devices. l

'Figf8 shows an arrangement similar to that of Fig. 7, except that the concentric resonant line is nowused to step up the voltage between the output of radio frequency stage 5| and the input of radio frequency stage 52.

The ratio. of stepdown or step up transformation is ,of course determined by the power consumption' in the following stage.

Fig. 9. illustrates, in perspective, a rear view of a pair of vacuum 'tubesn ii, 54 mounted on the outer conductor of my improved concentric line for minimizing lead connections between tube electrodes and condenser .plates 8, 9. The interposed or'sandwiched plates I, 9. are shown mounted on insulating supports 55. It will be' evident, of; course, that the metallic covers for M the unit have not been shown in order to expose the interior. Although the improved concentric line of the invention has been shown mpioying discs and cylinders, it will be understood that these elements may take different forms and be located at dliferent places between t conductors, and that various odiflcations may be made both in the line and associated circuit arrangements without departing from the spirit and scope of the invention. For example, the

condenser plates, as well as the plates capacitively coupled thereto, can be adiustably mounted to vary the spacing therebetween and between .same and the inner conductor.

What is claimed is:- V

1. A tuned high frequency circuit ner conductor comprising a pair of spaced rods arranged in the same straight line and having remote ends connected to said outer conductor, the adjacent ends of said rods being so spaced as to provide a capacitor, and a plurality'of parallel conducting plates placed between the adjacent ends of said rods insulated from each other and from inner and ,outer conductors, whereby they I provide terminal cbnnections for an associated circuit.

7 comprising concentric inner and outen-conductors, said inwith their planes a transverse to ,the longitudinal axis of said rods Y said plates being as 'to provide a capacitor, and a plurality of parallel conducting plates placed between the adjacent ends of said rods with their planes transverse to the longitudinal axis of said rods,

a said plates being insulated from each other and from inner andiouter conductors, whereby they provide terminal connections for anassociated circuit, at least two of ,said con ucting plates being wider than the normal width of said outer conductor. f I

4. A tuned high frequency circuit comprising concentric inner and outer conductors, said inner conductor comprising a pair of spaced rods i arranged in the same straight line and having inner and outer 2. A' tuned high frequency circuit comprising a "concentric inner and outer conductors, said vinner conductor comprising a pair of spaced rods arranged in the same straight line and having remote ends connected to said outer conductor,

the adjacent endsor said rods being so spaced.

asf'to provide acapacitor, and a plurality of parallel adjacent ends of transverse to the said rods with their planes longitudinal axis of said rods,

conducting plates placed between the remote ends connected to'said outer conductor, the adjacent ends of said rods being so spaced as to provide a capacitor, and a plurality of parallel conducting plates placed between the adjacent ends of said rods with their planes transverse to the longitudinal axis of said rods, said plates being insulated-fromeach other and from inner andouter conductors, whereby they provide terminal connections for anassociated circuit, a pair of said plates being on opposite sides.

of and substantially equally distant from a voltage nodal point ion the voltage distribution curve of said tuned circuit, said pair of plates being wider than the norinal width of said outerconductorfor minimizing lead lengths extending therefrom to said associated circuit.

5. A high frequency tuned oscillatory circuit comprising a container in the form of a substantiaily continuous metallic surface, a lumped capacitor within said surface, and a pair of,'inductance elements in the form of linear conductors devoid of concentrated reactance direct- 1y connecting said capacitor to said surface, said lumped capacitor including three or more condenser plates insulated from each other, at least two of said plates being insulated from said in:

ductance elements, said plates constituting ter minals for said tuned circuit.- 6. In a multi-stage high frequency system. a first push-pull stage comprising. a pair of electron discharge devices, asecond push-pull stage s also comprisinga pair of electron discharge devices, an interstage coupling element comprising a concentric resonant line composed of concentric inner and outer conductors, said inner conductor comprising'a pair of spaced rods arranged in the same straight line and having remote ends connected to said outer conductor, the adjacent ends of said rods being so spaced as to provide a capacitor, and a plurality of parallel conducting plates placed between the ends of said rods with their planes transverse to the longitudinal axisof said rods, said plates being insulated from each other and from inner and outer conductors, and connections from the output of said first stage and the input of said second stage to said parallel plates.

7. In a multi-stage high frequency system, a

connected to said outer conductor, the adjacent ends of said rods being so spaced as to provide a capacitor, and a plurality of parallel conducting plates spaced between the ends of said rods with 1 their planes transverse to the longitudinal axis of said rods, saidplates being insulated from each other and from the inner and outer conof said plates being on opposite sides of a voltage nodal point on said line, said pair of' plates being wider than the normal width of said outer conductor, connections from the grid electrodes of said oscillator tubes to said pair of plates, and

connections from the grid electrodes of said amplifier tubes to said pair of plates.

10. In a high frequency system, thecombination with a push-pull oscillator comprising apair of vacuum tubes exciting a, push-pull radio frequency amplifier also comprising a, pair of vacuum tubes,- of .a frequency controlling circuitin the form of concentric inner and outer conductors, said inner conductor comprising a pair of spaced rods arranged in the same straight line and having remote ends connected to said outer ductors, whereby they provide terminal con-.-

nections for said input and output circuits, said output circuit being connected to a pair .of said conducting plates equally spaced on opposite sides of the. electrical center of said resonant line, said input circuit also being connected to another pair of said conducting plates equally spaced on opposite sides of the electrical center oi said line, said first pair of plates being located farther away from said center than said last pair of plates, whereby said line acts as a voltage stepnected to said outer conductor, the adjacent ends of said rods, said plates being insulatedfrom down coupling element.

8. In a multi stage high frequency system, a

first push-pull stage comprising a pair of electron discharge devices, a second push-,pull stage also comprising a pair'of electron discharge devices, and an interstage coupling element' between the output of said first stage and the'input.

of said second stage, said elements comprising a concentric resonant line composed of concentric inner and outer conductors, said inner conductor comprising a pair of spaced rods arranged in the same straight line and having remote ends conof said rods being so spaced as to provide a capacitor, and a plurality of parallel conducting plates spaced between the ends of said rods with their planes transverse to the longitudinal axis each other and from inner and outer conductors, whereby they provide terminal connectionsfor said input and-output circuits, said output circuit being connectedto a pair of said conducting plates equally spaced on opposite sides of theelectrical center of said resonant line, said input circuit also being connected to another pair of said conducting plates equally spaced on opposite sides of the electrical center of said line, said first pair of plates being located nearer to said center than said last pair of plates, whereby said line acts as a'voltage step-up coupling element. a

9. In a high frequency system, the combination with a push-pull oscillator comprising a pair of vacuum tubes exciting'a push-pull radio frequency amplifier also comprising a pair of vacuum tubes, of a frequency controlling circuit in the form of concentric inner and .outer conductors, said inner conductor comprising a pair of spaced conductor, the adjacent ends of said rods being so spaced as to provide a capacitor, and a plurality of parallel conducting plates placed between the ends of said rods with their planes transverse to the longitudinal axis of said rods, said plates being insulated from each other and from the inner and outer conductors, whereby they provide "terminal connections for said vacuum tubes, a

pair of saidplates being on opposite sides of a voltage nodal point on said line, connections from the grid electrodes of said oscillator tubes to said pair of plates, and connections from the grid electrodes of said amplifier tubes to said pair of plates.

11. In a high frequency system, the combination with a push-pull oscillator comprising a pair ,of vacuum tubes exciting a push-pull radio frequency amplifier also comprising'a pair of tubes,

of afrequency controlling circuit in the form of concentric innerand outer conductors, said in- .ner conductor comprising a pair of spaced rods, arranged in the same straight line and having remote ends connected to said outer conductor, the adjacent ends of said rods being so spaced as to provide a capacitor, and a plurality'of parallel arranged in the same straight line and having remote ends connected to said outer conductor, the adjacent ends of said rods being so spaced as to provide a capacitor, and a plurality of parallel conducting plates placed between the ends of said rods with their planes'transverse to the longitudinal axis of said rods, said plates being insulated from each other and from inner and outer conductors, whereby they provide terminal connections for said vacuum tubes, a pair constituting terminals for say "13. In a high frequency s stem, the combinaconducting-plates placed between the ends of said rods with their planes transverse to the longitudinal axis of said rods, said plates being insu-' lated from each other and from inner and outer conductors, whereby they provide terminal con: nections for said vacuum tubes, a pair of said plates being on opposite sides of a voltage nodal point on said line, connections from the grid electrodes -of said oscillator tubes to said pair of plates, and connections from the grid electrodes of said amplifier tubes to said pair-of plates, and

means connected to said pair of spaced rods for modulating the energy available in said radio frequency amplifier.

. 12. A' high frequency tuned oscillatory circuit comprising a container in the form of a substantially continuous metallic surface, a lumped capacitor within said surface, and a pair of inductance elements directly connecting said capacitor to said surface, said lumped capacitor including three or more condenser plates insulated from each other, at least two ofsaid platesbeing insulated from said inductance elements, said plates tuned circuit.

tion with a push-pull oscillator comprising a pair of vacuum tubes exciting a push-pull radio frequency amplifier also comprising a pair of vacuum tubes, of a frequency controlling circuit in the form of concentric inner and outer conductors, said inner conductor comprising a pair of spaced rods arranged in the same straight line and having remote ends connected to said outer conductor the adjacent ends of said rods being so spaced and provided with plates as to form a capacitor, and a plurality of parallel conducting plates placed between the ends of said rods with their planes transverse to the longitudinal axis of said rods, said intermediate plates being insulated from each other and from theinner and outer conductors, a pair of said intermediate plates being on oPDOsite sides of a voltage nodal t point on said line, connections from the input electrodes of said radio frequency amplifier to output electrodes of said oscillator to certain of said other plates.

14. In a high frequency system, the combination with a first push-pull driving stage compris-' ing a pair of vacuum tubes, and a second pushpull driven stage also comprising a pair of vacuum tubes, of an interstage coupling element between' the output of said first stage and the input of said second stage, said element comprising a concentric resonant line composed of concentric inner and outer conductors, said inner conductor comprising a pair of spaced rods arranged in'the same straight line and having remote ends con-.

nected to said-outer conductor, the adjacent ends of said rods being so spaced as to provide a capacitor, and a plurality of parallel conducting plates said' pair of plates, and connctionsfrom the pair of spaced rods arranged in the same straight quency circuit comprising concentric iimer and outer conductors, said inner conductor comprising a pair of spaced rods arranged in the same straight line and having remote ends connected to said outer conductor, the adjacent ends of said rods being so spaced as toprovide a capacitor,

of connections extending from correspondin electrodes of said vacuum tubes to' a pair of said plates.

16. In a high frequency system, the combination with a push-pull driving stage exciting a push-pull driven stage,.O a tuned high frequency circuit comprising concentric inner 'and outer conductors, said innerconductor comprising a on said tuned circuit, connections from the input electrodes of said driven stage to said last pair "of plates, and connections from the output electrodes of said driving stage to certain other plates of-said plurality.

NIL-5 E. LINDENBLAD. 

